= Solution
Use the standard local <chemical quench level> approximation: <carbon monoxide>-rich gas from the hot deep region is transported upward, and conversion becomes slower as the gas enters the cooler layers. Assume that neither a faster loss process nor strong compositional fractionation removes <carbon monoxide> above the quench level. For an effective mixing length $L$, the <eddy mixing time> is $\tau_{\rm mix}\simeq L^2/K_{zz}$, so outrunning conversion near $1\,\mathrm{bar}$ requires
$$
\boxed{K_{zz}\gtrsim\frac{L^2}{10^5\,\mathrm{s}}}.
$$
The usual order-of-magnitude choice is $L\simeq h_b$, the local <atmospheric scale height> at $T_b=1400\,\mathrm{K}$. Equal planetary mass and radius give the same gravity as <Jupiter>; with the same <mean molecular weight>, the <atmospheric scale height> scales linearly with <temperature>. To use the supplied $30\,\mathrm{km}$ reference, additionally adopt a representative Jovian reference <temperature> $T_J=150\,\mathrm{K}$. Then
$$
h_b\simeq30\,\mathrm{km}\frac{1400}{150}\simeq280\,\mathrm{km},\qquad
\boxed{K_{zz}\gtrsim8\times10^5\,\mathrm{m^2\,s^{-1}}\simeq8\times10^9\,\mathrm{cm^2\,s^{-1}}}.
$$
Using $k_BT/(\mu m_Hg)$ directly with $\mu\simeq2.3$ and Jovian $g\simeq25\,\mathrm{m\,s^{-2}}$ gives $h_b\simeq200\,\mathrm{km}$ and $K_{zz}\gtrsim4\times10^5\,\mathrm{m^2\,s^{-1}}$, the same order of magnitude. The supplied Jovian height is approximate and does not specify its reference <temperature>. Inserting $30\,\mathrm{km}$ unchanged for the hot gas would instead give $9\times10^3\,\mathrm{m^2\,s^{-1}}$ and neglect this temperature scaling.
The pressure separation is relevant to a stronger, whole-column transport estimate. With constant gravity and <mean molecular weight>, the profile gives
$$
\begin{aligned}
\Delta z&=\int_{10^{-3}\,\rm bar}^{1\,\rm bar}h(P)\,d\ln P\\
&=\frac{30\,\mathrm{km}}{150\,\mathrm{K}}\left[\frac{1400+500}{2}\ln100+500\ln10\right]\simeq1.1\times10^3\,\mathrm{km}.
\end{aligned}
$$
If one additionally requires diffusion through the entire column within $10^5\,\mathrm{s}$, a sufficient conservative condition is $K_{zz}\gtrsim\Delta z^2/\tau_{\rm chem}\sim10^7\,\mathrm{m^2\,s^{-1}}$. It is not a necessary local quench condition: the <chemical relaxation time> is expected to become much longer in the cooler gas, so a longer total transit time can still preserve <carbon monoxide>.
\b[The usual quench estimate is $K_{zz}$ of order $10^6\,\mathrm{m^2\,s^{-1}}$ under the stated scale-height assumptions.] A unique bound for survival to $10^{-3}\,\mathrm{bar}$ cannot be inferred from one reaction time without assumptions about its variation, the mixing length and upper-atmospheric losses.
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